The invention relates to telecommunication networks and particularly to mobile networks using ATM (Asynchronous Transfer Mode) transfer systems. The invention also relates to the control of mobility and call control functions in ATM systems.
Two of the current development trends in telecommunication are mobile communication and broadband networks. The term broadband typically refers to a bit rate higher than 2 Mbit/s. Narrowband usually refers to a bit rate of 64 kbit/s or lower. Bit rates from 64 kbit/s to 2 Mbit/s are sometimes referred to as wideband. Broadband networks are attractive for at least two (compatible) reasons:
1) A single broadband network bearer divided among a plurality of users, few or none of whom need the whole bandwidth alone, can offer advantages concerning flexibility and the building of transfer systems.
2) Information to be transferred on separate transfer channels possibly demand broadband channels. Users need new high-quality services, which in turn require high bit rates. Such services include e.g. video conferences, high-speed data transmission, etc. A common denominator for these services is multimedia, which combines image, voice and data into one service.
Due to its numerous strengths, ATM (Asynchronous Transfer Mode) is chosen as the transmission technique in various standardized B-ISDN (Broadband Integrated Services Digital Network) protocol structures. In this connection the term xe2x80x98transmissionxe2x80x99 refers to the use of ATM switching and multiplexing techniques in a data link layer (i.e. an OSI Layer 2, hereinafter referred to as an ATM layer) relaying end user traffic from a source to a destination within a network. Between the source and the destination are established virtual connections, which requires the network to have switching functions. Signalling and user information are normally conveyed by different virtual connections in an ATM layer. A virtual connection is identified in the ATM layer by a Virtual Path Identifier VPI and a Virtual Channel Identifier VCI.
In ATM information is conveyed segmented in fixed-length cells, the number of the cells in a time unit being proportional to the user""s bandwidth requirements. Each 53-octet cell is divided into a 5-octet header and a 48-octet information field, as shown in FIG. 2.
The main purpose of the header is to identify a connection number for a cell sequence providing a virtual channel for a particular call. A plural number of virtual paths, which are multiplexed in the ATM layer, can be connected to one and the same physical layer (i.e. an OSI Layer 1), each path being identified by an 8-bit VPI at a User-to-Network Interface UNI and a 12-bit VPI at a network-node interface. Each path can comprise a plural number of virtual channels, each of which is identified by a 16-bit VCI. The header can also comprise other fields, such as a Header Error Control HEC, a Generic Flow Control GFC, a Cell Loss Priority CLP and a Payload Type PT.
The User-to-Network interface UNI between an ATM user terminal and an ATM switch (a private UNI) and between private and public ATM networks (a public UNI), together with a UNI signalling (and an ATM cell) related thereto, are defined at least in the following recommendations:
[1] ATM User-to-Network Interface Specification, version 3.1, ATM Forum, 1994;
[2] ATM User-to-Network Interface (UNI) Signalling Specification, version 4.0, ATM Forum, June 1994;
[3] ITU-T Recommendation Q.2931 (1994) Broadband Integrated Services Digital Network (B-ISDN), Digital Signalling System No. 2 (DSS 2), User-to-Network Interface (UNI) Layer 3 Specification for Basic Call/Connection Control. ITU-T.
In mobile networks, radio interfaces have conventionally been narrowband. Mobile network transmission systems have conventionally been implemented with circuit-switched connections using a star or tree network configuration. In order to increase the capacity and flexibility of transmission systems, different broadband packet switched transmission systems have also been proposed for mobile networks, e.g. in WO 9319559, WO 9400959 and EP 0366342. EP0426269 describes a mobile system in which base stations are connected via routers to ATM network switches. Virtual connections controlled by the base stations are established between the base stations through the ATN network. Elementary mobility management is based on routing tables, which are maintained at base stations and in ATM switches and updated as subscribers move. GB2268359 and EP 679042 describe an ATM-access network in which there are permanent ATM virtual connections (to speed up the call set-up) between base stations and a mobile network interface, said connections being allocated for each call separately.
A possible future development trend is that mobile systems will have a broadband radio interface. In this case the transmission system of the mobile system should also be broadband, a potential alternative being provided by the ATM technology.
A third development trend is the introduction of wireless data transmission (wireless ATM) and mobility management into ATM networks. However, a problem arising from this is that current B-ISDN and ATM standards in no way support the mobility management, subscriber authentication, call control, etc., required by mobile communication. To introduce into the ATM network such supplementary characteristics required by mobile communication would therefore seem to require considerable development and standardization of and significant changes to the existing ATM systems. The implementation of wireless ATM would thus become a slow and an expensive process.
An object of the invention is to implement an ATM-transmission or an ATM-access network in a more flexible manner than before in mobile network architectures that conventionally use circuit-switched transmission systems.
Another object of the invention is to add wireless transmission and mobility to the ATM network, without significant changes to the existing ATM networks and standards.
An aspect of the invention is a telecommunication network, such as a mobile network, comprising mobile stations, base stations, at least one switching network element performing call control and switching, and an ATM switching function for a dynamic switching of virtual ATM transmission connections between the base stations and said at least one switching network element. The invention is characterized by said ATM switching function being arranged in said at least one switching network element and being controlled through an internal interface by a call control of the network element.
Another aspect of the invention is a wireless ATM network comprising mobile stations and at least one ATM switch to which base stations are connected through a network-to-user interface UNI. The invention is characterized by
the ATM network having at least one switching network element of another telecommunication network, such as a mobile network, to perform call control and switching control;
said switching network element being provided with an ATM switching function, which is controlled through an internal interface by the call control of the network element, for a dynamic switching of virtual ATM transmission connections between the base stations and said at least one switching network element.
A further aspect of the invention is a switching network element of a mobile network. The invention is characterized by the network element comprising an ATM switching function for a dynamic switching of virtual ATM transmission connections to base stations and by controlling the ATM switching function, through an internal interface, with a call control of the network element.
A still further aspect of the invention is a method according to claim 11.
In the invention a network element of a telecommunication network, such as a mobile network, which in conventional telecommunication network architecture performs the switching of circuit-switched connections, is provided with an ATM switching function. ATM switching functions are controlled by the same call control and switching control functions that are conventionally used e.g. for controlling a TDM switching field in a PLMN network element (Public Land Mobile Radio). In a minimum implementation, an ATM switching field provided with a suitable control interface is simply arranged in place of or parallel with the TDM switching field. The switching network element can thus be made, from the point of view of a physical and a logical interface layer, into one of the nodal points of the ATM network. As regards for instance PLMN-level signalling, mobility management and call control, the change is a transparent one, so said functions can be carried out applying solutions based on existing mobile networks and PLMN network elements, with only slight modifications. This reduces costs and enables even existing PLMN networks to be provided with an ATM transmission system. The invention also makes continuous evolution of the transmission system in telecommunication networks possible, because the use of ATM transmission can be further extended to other network elements, without changes being needed to higher level system solutions.
A telecommunication network element of the invention may comprise both a conventional TDM switching field and a new ATM switching field parallel with each other. This provides an advantageous solution for instance in a network evolution phase in which the telecommunication network comprises base stations or other network elements using both circuit-switched transmission and ATM transmission. The switching network element can in this situation be arranged to switch either a virtual ATM connection or a circuit-switched connection to a base station or other network element, depending on whether said base station or other network element supports ATM transmission or not.
The telecommunication network element of the invention functions in ATM layers according to ATM standards, signalling with other ATM devices (user terminals or ATM switches) in accordance with e.g. UNI signalling. The invention thus requires no changes to the ATM network signalling and its operation.
PLMN network elements of the invention can also be used for introducing mobility management and call control into a wireless ATM network. One or more PLMN network elements are arranged as a part of the ATM network and call control signalling is transparently transmitted through the ATM network. Since also the switching of virtual connections is performed in the PLMN network element, the rest of the ATM network is not required to have any features related to mobility management.
In a preferred embodiment of the invention, the PLMN element is connected to the ATM network through a UNI interface. The base stations are correspondingly connected to the ATM network through a UNI interface. The configuration of the ATM network can vary considerably. For instance, it is possible that each base station is connected through a UNI interface direct to a mobile services switching centre by an ATM switching function. For the mobile services switching centre the base stations are then ATM user terminals to which virtual connections can be switched. It is also possible that the base stations and the mobile services switching centre are connected to a base station controller by an ATM switching function through a UNI interface. For the base station controller the base stations and the mobile services switching centre are then ATM user terminals between which virtual connections can be switched. Both a mobile services switching centre and a base station controller may simultaneously comprise an ATM switching function.
The invention allows all special network elements and special functions related to wireless communication to be implemented into cellular radio networks using previously designed network elements and solutions. The designing of special solutions for a wireless ATM is thus avoided. The cellular network elements concerned are connected to the ATM network through a standard UNI interface, but the signalling between the cellular network elements takes place either transparently through the ATM network via said permanent virtual connections or separate signalling connections. The signalling related to wireless communication thus causes no changes in a standard ATM UNI protocol.